In motion picture projectors, motion picture film is intermittently advanced through a gate having a projection aperture. The film is moved or advanced until a frame is in alignment with the projection aperture and then held stationary for a discrete period of time during which light is passed during two discrete time periods through the aperture, film frame, and then a focusing lens, and onto a screen. This is followed by movement of the film until the next frame is in alignment with the projection aperture. This cycle of movement followed by a stationary period typically occurs 24 times each second.
One problem associated with the use of motion projectors is the problem of vertical picture steadiness, typically referred to as picture "jump". Picture "jump" is manifested by a slight blurring of the picture on the screen which is particularly noticeable at horizontally extending lines on the screen.
Although reducing picture jump to below one-third of one percent of the picture height has happened many years ago, obtaining less than one-fourth of one percent has been difficult and has been set as the industry's standard. Many types of mechanical designs have been made over the years to reduce the picture jump. However, picture jump has not been fully understood nor has it been eliminated.